#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m;
int t[N], v[N];
int a[N];
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> n;
  rep(i, 1, n) cin >> t[i] >> v[i];
  rep(i, 1, n) { a[i] = max(0, a[i - 1] - (t[i] - t[i - 1])) + v[i]; }
  cout << a[n];
  return 0;
}